The hard alloy material has characteristics of high hardness, high strength, good wear resistance, good corrosion resistance, low thermal expansion coefficient and high chemical stability. Even at high temperature, the hard alloy material still has high hardness, which is widely applied to various kinds of the products such as mechanical processing, metal mould, cutting tools, etc. For the practical application of hard alloy material, it is desired to choose a hard alloy material with the high hardness and wear resistance outside, and with the high ductility inside for bearing an external impact and stopping the crack propagation from the surface to the center. However, the conventional hard alloy material possesses the consistent physical and mechanical properties, from the outer surface to the inside of the material.
Various modifications on the hard alloy materials have been studied and proposed. For example, single layer or multi layers (as a coating layer) made of material with high hardness and good wear resistance are deposited on the surface of an alloy (as a base) by chemical vapor deposition (CVD) or physical vapor deposition (PVD), thereby forming a hard alloy with a ductile core and a hard surface by using different materials. However, there is an interface between the coating layer and the base of this hard alloy. Different thermal expansion coefficients of different materials have considerable effects on the performance and life of product manufactured by this hard alloy.
With advancements in technology and requirements of hard alloy quality of the applications, it is one of important goals to improve the physical and mechanical properties of the alloy materials, with not only the hard surface and the ductile inside but also the extended product life and the progress in performance.